Check around for "40g Breeder" tanks - I think they're a good match for your proposed dimensions, right off the shelf.
I agree, I did the same. this is more important if this is going to be 1/4" thicknes or over as hand grind only work good for thiner glass. They will charge you per yard but it will be worthy at all.you should call some local glass shops and get some qoutes! machine edge is the way to go...is this going to be braceless?.....